China has been blamed for a number of attacks on American corporate networks, most notably that of newsrooms from Bloomberg to The New York Times. It was The Washington Post (WaPo) that later reported that the attacks were traced to computer servers located in China. However, sophisticated cyber attacks can be launched from anywhere in the world, and cover their tracks by using remote servers.

According to WaPo, Mandiant, a computer security company, said in a report released to reporters this week that over the course of several investigations it found evidence that Chinese hackers had stolen e-mails, contacts and files from more than 30 journalists and executives at Western news organizations, and had maintained a “short list” of journalists for repeated attacks. Among those targeted were journalists who had written about Chinese leaders, political and legal issues in China and the telecom giants Huawei and ZTE, WaPo reported.

On Tuesday, the Chinese National Defense Ministry said in a statement that the government was not behind any cyber attacks against the United States.

"The Chinese army has never supported any hacking," the Ministry of National Defense said in a statement. "Such accusations are unprofessional and false," it added.

The ministry's remarks were in response to Mandiant's report that claimed China's army controls some of the most prolific hackers in the world, and that a host of cyber attacks had been traced to a building in Shanghai. According to Mandiant, the attacks were made against 141 companies, including 115 in the United States as far back as 2006.

"Cyberattacks are transnational, anonymous and deceptive with its source often difficult to be identified. Releasing irresponsible information will not help solve problems," Geng Yansheng, spokesman with Ministry of National Defense said in a briefing.